CB Receptors can become saturated with prolonged use. A 48 hour reset every 8-10 weeks is encouraged. However, ask your doctor first- some situations are too critical to risk this unsupervised.
Medical Cannabis: A Guide for Patients, Practitioners, and Caregivers:
Dr. Michael Moskowitz, a veteran pain management doctor, explains both the science and his experiences in a very well written book that is accessible to the layman.